Our long-term goal is to achieve a dramatic improvement in the sensitivity of biomedical EPR measurements. The approach is to design dielectric inserts to be used with standard commercial cavity resonators. Our hypothesis is that an insert made of appropriate materials and having appropriate dimensions can redistribute the microwave field within a cavity in a way that substantially increases the filling factor and microwave magnetic field intensity uniformly over the sample, increasing EPR sensitivity by as much as an order of magnitude. The primary emphasis of this pilot project is to design dielectric inserts that enhance sensitivity in specific applications to muscle research. Given the rapid growth of EPR in biomedical research, especially in site-directed spin labeling and high-frequency EPR, the proposed developments will have immediate impact on modem biomedical EPR measurements. This proposal is a logical extension of previous work that has demonstrated the remarkable enhancement of sensitivity of EPR measurements of spin labeled muscle fibers by ferroelectric KTaO3 insert in standard EPR cavities. Four specific aims will be addressed: (1) Develop methods for calculating the resonant frequency and microwave field distribution of an EPR cavity containing a dielectric insert, and manufacture the designed insert. (2) Modify the designs in Aim 1 for specific application important for muscle research: sample orientation parallel to the external magnetic field. (3) Perform control measurements to evaluate the physical performance of the insert. (4) Measure the improvement of signal intensity for biological samples, especially for spin-labeled muscle proteins and muscle fibers. This pilot project will emphasize the development of reliable computational methods for designing sensitivity-enhancing inserts and to demonstrate experimentally that these methods work for typical muscle research applications. This will lay the foundation for future systematic development of sensitivity enhancements for biomedical EPR research, bringing the high resolution capabilities of EPR to the analysis of complex molecular structure and dynamics in a wide range of previously inaccessible biomedical problems. [unreadable] [unreadable]